DESCRIPTION (Author's Abstract): The present proposal tests the hypothesis that age-related declines in inhibitory function account for age differences in selective attention. Attention is a complex function of the nervous system involving a balance between the processes of facilitation and inhibition. It is postulated here that aging is associated with changes in the inhibitory control of behavior and age-related deficits in attentional functioning represent a disruption of the balance between facilitatory and inhibitory processes. The series of experiments in the present proposal was designed to examine the role of inhibitory processes in age differences in attention. Three experiments involve psychophysiological measures of attention in the autonomic nervous system. These studies are intended to examine physiological processes of habituation and inhibition, using orienting paradigms in which the autonomic orienting response is taken to reflect the allocation of attention. If the model of age-associated decline in inhibitory function is valid, this decline should be evidenced by reduced habituation to irrelevant information on the part of older adults. Three further experiments examine age differences in inhibitory processing in the context of the negative priming paradigm. The phenomenon of negative priming depends on efficient inhibitory processes, and so allows the straightforward prediction that older adults should exhibit reduced negative priming, or even none at all. The body of work proposed here tests a specific hypothesis about the locus of age differences in attentional functioning, and thus can make an important contribution to scientific understanding of aging and selective attention.